Staphylococcus aureus nosocomial infections in critically ill patients admitted in intensive care units

BACKGROUND AND OBJECTIVE: To investigate the frequency of nosocomial infections caused by Staphylococcus aureus in critically ill patients admitted to Spanish intensive care units (ICUs) and to describe the characteristics and outcome of patients in whom this pathogen was isolated. PATIENTS AND METHOD: Prospective, observational, and multicenter study. All patients admitted during one or 2 months to the participating ICUs in the National Nosocomial Infection Surveillance Study (ENVIN) between 1997 and 2003 were included. Patients were classified as infected by S. aureus, infected by other microorgaanisms and without nosocomial infection. RESULTS:A total of 34,914 patients were controlled of whom 3,450 (9.9%) had acquired a nosocomial infection during his/her ICU stay (16.0 infections per 100 patients). In 682 (19.8%) patients, a total of 775 infectious episodes in which one of the microorganisms isolated was S. aureus were documented (cumulative incidence 2.2 episodes of S. aureus, infection per 100 patients). There was a predominance of S. aureus, infection in patients with pneumonia associated with mechanical ventilation (21.4%) and in patients with catheter-related bacteremia (13%). Independent variables associated with S. aureus infection were male sex (odds ratio [OR] = 1.25; 95% confidence interval [Cl], 1.03-1.52) and underlying trauma pathology (OR = 1.72, 95%; 95%Cl, ' 1.26-2.35), whereas an older age has been a protective factor (OR = 0.90; 95%Cl, 0.84-0.96). Mortality in patients with S. aureus infection was significantly higher than in infections caused by other microorganisms, and in both cases higher than in patients without infection (34.5%, 30.3%, and 10.7%, respectively). In 208 (30.5%) patients, infections due to methicillin-resistant S. aureus were diagnosed, which in turn had increased significantly over the years (p = 0.001). Mortality in patients with methicillin-resistant S. aureus infection was 35.1% compared with 34.2% in patients with methicillin sensitive S. aureus infections (p = NS). CONCLUSIONS: S. aureus was isolated in 19.8% of patients with ICU-acquired infection, particularly in relation to pneumonia in mechanically ventilated patients. Mortality in patients with S. aureus infection was higher than that in patients with infections due to other microorganisms and patients without infection. In contrast, differences in the outcome of patients with infections caused by methicillin-sensitive or methicillin-resistant S. aureus; were not found.